Refractory roof



Oct. 24, 1961 R. P. HEUER 3,005,422

REFRACTORY ROOF Filed Nov. 2a. 1958 INVENTOR flzpssefc Rearce Hews?ATTORNEY S i ate vania Filed Nov. 28, 1958, Ser. No. 776,885 4 Claims.(Cl. 110-99) The present invention relates to refractory roofs of thecharacter employed in metallurgical furnaces such as open hearth steelfurnaces, copper refining furnaces, and the like.

The present application is a continuation-in-part of my copendingapplication Serial No. 408,897, filed February 8, 1954, for RefractoryRoof which is now abandoned.

A purpose of the invention is to reduce the pronounced tendency of basicrefractory roof brick to spall parallel to the hot face.

A further purpose is to provide roof brick having internal oxidizablemetallic plates which are comolded into the brick and extend at leastover a major portion of the longitudinal dimension of the brick, and toplace such bricks in a curved arch of the brick.

A further purpose is to dispose the internal plates substantiallyradially in a curved arch.

A further purpose is to construct a curved arch having means of supportfor the brick and internal oxidizable metallic plates which are comoldedinto the brick and extend at least over a major portion of thelongitudinal dimension of the brick.

A further purpose is to dispose the internal plates substantiallyradially in a curved arch together with external plates in thetransverse joints of the roof placing the external plates on the bricksby comolding or by introducing the plates at the time of assembly.

Further purposes appear in the specification and in the claims.

In the drawings I have chosen to illustrate a few only of the numerousembodiments in which my invention may appear, selecting the forms shownfrom the standpoints of convenience in illustration, satisfactoryoperation and clear demonstration of the principles involved.

FIGURE 1 is a fragmentary diagrammatic section transversely of asuspended roof arch according to the invention.

FIGURE 2 is a fragmentary section in the position indicated by the line22 of FIGURE 1, substantially in plan.

FIGURE 3 is a fragmentary diagrammatic vertical section in thetransverse direction through a modified arch of the invention.

FIGURE 4 diagrammatically represents a radial joint in a refractoryroof, in which joint are an oxidizable metallic plate and an asbestosseparator, the latter occurring near the hot end of the joint.

Describing in illustration but not in limitation and referring to thedrawings;

Basic refractory brick have been employed in roof construction withoxidizable metallic spacer plates applied on all faces. As the furnacecontinues in service, the metal of the spacer plate, which is usuallyiron or steel, oxidizes, and the iron oxide reacts with the basicrefractory of the brick at either side, which is usually of chromite,magnesia or a mixture of the two predominating in either of thecomponents. This tends to integrate the roof together, preventingleakage of gases at the joints, preventing infiltration of air, andreducing the tendency of the brick to crack and spall.

The metallic pacer plates in the joints may have one objection in thatthe oxidation which occurs in service increases the thickness of theplates by percent or more. Furthermore, the oxidation is not uniformthroughout the length of the brick since itis practically negligible atthe cold face and increases with increasing distance toward the hotface. This non-uniform degree of oxidation causes non-uniformdimensional changes in the brick which may localize the strains in acurved arch and concentrate them at or near points where oxidation hasbeen the greatest.

Difiiculty has been encountered in sprung arches, in suspended archesand in combined sprung arches and suspended arches if the tendency ofthe arch to elongate in the direction of the are when the plates oxidimat the radial joints is excessive. This develops a com paratively highand localized pressure in the direction of the arc, subjecting the brickto high compression forces which may cause failure or cracking.

The basis refractory brick of the character which have previously beenused with oxidizable metallic plates on the lateral faces have shown atendency to spall along a line parallel to the hot face and at adistance of one to three inches from it.

I have discovered that if an oxidizable metallic plate is comolded inthe interior of the basic brick containing at least 10 percent ofmagnesia, and extends longitudinally of the brick throughout the majorportion of the length of the brick, a wholly different and moreadvantageous behavior occurs. As the plate which is buried in the brickby comolding oxidizes, it does not cause any overall dimensional change.It appears that the iron oxide formed by the oxidation of the platereacts with the basic ingredients of the refractory, for example withthe magnesia present in the refractory, to form magnesioferrite, whichdiffuses into the refractory without causing an overall volume change.The same thing occurs in a brick of chromite where the magnesia contentexceeds 10 percent by weight.

I have also discovered that the oxidizable metallic spacer plate whichextends throughout the interior of the brick exerts a pronouncedtendency to prevent spal-ling oif of the hot ends of the brick. Thiswould appear to be due to the fact that the magnesioferrite is highlyrefractory and tends to create a strengthening rib running lengthwisethrough the brick, and also the magnesioferrite tends to break up theforce distribution and pre vent crack propagation across from one sideto the other of the magnesioferrite band.

To be most effective the buried plate should extend almost to the hotface or preferably to a distance not in excess of one inch from it. Itis less important that the plate extend to the cold end, although it isdesirable to extend to a position close to the cold end.

The number of plates which are buried in the interior of the brick bycomolding may vary. In some cases a single plate is suflicient, althoughin other cases two or more plates extending in the longitudinaldirection will be used.

External plates are used on the joints in the transverse direction. Theplates on the transverse faces are conveniently comolded with the brick,although they will in some cases be assembled to the brick when the roofis made. The plates which are comolded on the transverse faces performthe desirable function of strengthening the brick during shipment.

A considerable amount of testing experience has now been had with theimproved basic refractory roof of the present invention applied to openhearth furnaces. For example, one open hearth furnace is oil fired andhas a regular capacity of 3 50 tons. Previously the main roof of thisfurnace was equipped with so-ca-lled Zebra construction of alternaterows of basic and acid refractories, and the balance of this roof wassilica. The

Zebra roof would last approximately 140 heats with extensive patchingand repairs, after which the entire roof required replacement. The mainroof of this furnace was constructed to eliminate silica bricks by usingbasic bricks comprising a mixture of chrome ore and magnesite, eachbrick being of key shape and molded to have steel plates approximatelyinch thick on four major external surfaces and internal plates disposedalong the major axis of the brick in two planes radial of the arch whichwere spaced approximately equidistant from each other and from adjoiningsurfaces of the brick.

These bricks were laid in an arch formed between fixed skewbacks. Theroof was 12 inches thick with 15 inch ribs. Allowance for expansion wasmade in the radial joints at the hot face of the brick by insertion ofasbestos strips two inches wide and inch thick placed between alternatecourses of the brick for a distance approximately six feet out from eachskewback, and in every fourth course of brick for the remaining fourteenfeet of the arch. The percentage of expansion allowance represented bythe asbestos was approximately 0.6 percent measured along the curvedinner surface of the arch between the skewbacks.

Prior to the installation of this roof I learned that because of theincreased cost of the basic refractory it would be necessary for theroof to last slightly more than 200 heats in order for it to beeconomical as compared to the best prior art roofs.

The roof of this furnace has the following features:

(1) The arch is sprung from rigid skewbacks, the arch length being 24feet between skewbacks.

(2) There are steel plates on the radial faces of the basic refractorybrick.

3) There are internal plates extending radially in the basic refractorybrick.

(4) Between the hot ends of the basic refractory brick, asbestos sheetis introduced.

The roof of this new open hearth furnace stood up for approximately 180percent of the minimum requirement of heats.

Since the success of this first basic open hearth furnace, there hasbeen a major change to basic open hearth roofs in accordance with thepresent invention.

More than 60 open hearth furnaces have been converted to the basic archroof of the present invention since the beginning of the year 1958. Someof these furnaces are located in typical steel plants in Wierton, WestVirginia; Detroit, Michigan; Buffalo, New York; Cleveland, Ohio;Chicago, Illinois; Peoria, Illinois; Homestead, Pennsylvania and Geneva,Utah.

There are several opposing forces which lead to the surprising behaviorof the open hearth roof of the present invention. In order to understandthis behavior, I will compare with the practice using wire screen, meshor gauze at the radial joints according to my US. Patent 2,779,233. Ihave had considerable experience with the type of roof which uses thewire screen, mesh or gauze at the radial joints in Europe.

(1) Continuous steel plates in the radial joints of a sprung arch basicrefractory roof in accordance with the present invention unite thebricks in the line of the arc of the roof to form a monolithic orintegrated structure, which greatly strengthens the arch and guardsagainst portions of individual bricks dropping out prematurely.

(2) Where the continuous steel plates are used in the radial joints ofthe sprung arch, the steel plates expand due to formation of iron oxide,which has a lower density than iron. If nothing else is done, therefore,the presence of continuous steel plates in the radial joints causes aplus dimensional change or a dimensional increase.

(3) The steel screen, mesh or gauze in the radial joints, when itoxidizes, does not form a monolithic structure. The reason for this isthat the basic brick surface and the intervening gauze only make contactalong the surfaces of the wires and tlr's surface contact is notsufficient to bond the structure monolithically.

(4) When the steel mesh, screen or gauze in the radial joints oxidizes,the oxide formed does not cause a dimensional increase but diffuses intoand reacts with the basic refractory and the net result is a minusdimensional change or a dimensional decrease in the direction of the arcof the arch.

(5) Asbestos layers between the radial joints at the hot end cause a netdimensional decrease or a minus dimensional change.

Summarizing the above, the steel wire screen, mesh or gauze isunsatisfactory because it does not produce a monolithic joint at theradial joints. The continuous plate at the radial joints produces amonolithic joint but when used alone it has the undesirable feature ofcansing a dimensional increase. By using the internal plates which alsoextend radially it is possible to avoid a plus dimensional change whenboth the external and internal plates oxidize, because as mentionedabove the internal plate forms iron oxide which reacts with the magnesiato form magnesioferrite, and the magnesioferrite diffuses into therefractory which produces a minus dimensional change.

Thus it is possible to use rigid skewbacks, and even if spring loadedskewbacks are used, the need for dimensional adjustment would not besubstantial.

On the other hand, if steel screen wire, mesh or gauze were used at theradial joints, there is a minus dimen sional change and the radialjoints are not monolithic.

Considering now the curved arch as shown in'FIG- URES 1 and 2, I thereillustrate suitably shaped overhead steel supporting members 25 runningin the arc direction, and receiving and supporting at intervals T-shapedhangers 26 having hooked upper ends 27 engaged over the supportingelement, and having opposed projections 28 at the lower ends which arereceived within hanger openings 34) of the respective brick. It isimmaterial from the standpoint of the present invention whether thehanger recesses 39 are of the character which are entirely formed ofrefractory, entirely formed of metal imbedded in the refractory, orformed of a combination of the two.

Basic refractory roof brick 31 suspended from the hangers are alsopartially supported by skewbacks 32 as well known (only one skewback isshown). The skewbacks may be backed up by springs as is well known (notshown).

Each of the brick 31 has radial faces 33, transverse faces 34-, hot ends35, and cold ends 36. The brick are wedge shaped as shown in 'FIGURE 1.

Extending in the radial direction through the basic refractory brick andimbedded or buried therein by co molding with the refractory is anoxidizable metallic plate 37. When a single plate is used it ispreferably located in the middle. The plate 37 (as where formed ofaligned plate portions 37a and 37b as indicated in FIGURE 2) preferablyextends over the major portion of the length and width of the brick andis in no respect comparable with separate wires or a mere screen mesh.The plate extends desirably to about one inch from the hot end, and thisdistance should not exceed 5 inches.

The plate 37 will normally extend to the hanger socket which is adjacentthe cold end and will if required be cut out to avoid the hanger.

The plates 37 are of any suitable oxidizable metal, preferably low alloyor plain carbon steel, but permissibly also stainless steel. The platethickness will normally be less than inch and preferably between andinches.

In the preferred embodiment the internal plates are comolded with therefractory. External plates 38 are provided on those faces of the brickwhich are placed in the transverse joints. The external plates coverapproximately the full width of the brick and the pre.

ponderance of the distance between the hot face and the cold face. Theinternal plates are preferably in two approximately equal pieces 37a and37b, which pieces are supported by external plates on opposite faces ofthe brick and the pieces extend into the refractory toward each otherfrom these external plates as by welded afl'lxation to the externalplates. The external lates are preferably the same material as theinternal plates, their thickness being less than 4 inch and preferablybetween and 7 inch. Instead of a welded assembly of the internal andexternal plates, it is also desirable in some cases to use a singleplate formed to provide an external portion and an internal portiondisposed at a right angle to each other.

When the molding operation is effected, one external plate withpreferably attached internal plate or plates protruding upward, isplaced in the bottom of the mold and the refractory mixture is placed ontop of it in the mold. The other external plate with its internal plateor plates protruding downward is placed in the top of the mold oralfixed to the top die of the molding press.

The pressing operation is completed by pressing upon the external platesto comold the refractory to the plates. The internally molded plates canif desired be placed approximately radial and so located in the backthat in the assembled roof the distance between the internal plates inthe direction across the arch of the furnace is approximately uniform.

It is not necessary that the external plates be placed perpendicular tothe internal plates. Internal plates can be placed in a position atright angles to movement of the molding die and parallel to the externalplates if any are present. In such case the external plates would beplaced in the mold first, then part of the refractory mixture, then aninternal plate, then more refractory mixture, etc. until the desirednumber of plates have been included in the mold with the final externalplate on the top. This molding procedure is not so easily affected asthe molding process with vertical internal plates, nevertheless, thebrick is quite suitable for the purpose.

The number of internal plates may be varied and the number should beincreased as the size of the brick increases. For general uses I preferbrick of cross-section 6 x 3 inches or smaller, as for example 4 x 2 /2inches. In cases where the pair of opposed internal plates extendsthrough the minor dimension of the brick, such as the 2 /2 inchdimension of 4 /2 x 2 /2 inch brick, I have found that two pairs ofopposed plates spaced 1 /2 inches apart and 1% inches from each lateralface are satisfactory. For best results the distance from the internalplate or plates to the nearest lateral face should not exceed 2 /2inches.

By using internal plates within the brick which are disposed in a radialposition in a curved arch, I find that I have many choices of the methodof treating the radial joints themselves. A single loose plate may beinserted between the brick in the radial joint or in way of furtherillustration plates may be pressed on every brick or on alternate brick,thereby providing a single or double thickness of metal in the radialjoint.

As shown in FIGURE 4, the brick 21 has on the radial face a loose plate54 which hooks at 55 over the cold end 36, and extends to a point 56which is suitably an inch or more removed from the cold end 35. A stripof asbestos paper 58' is disposed over the radial face be tween thebrick at the hot end. Loose oxidizable metallic plates, or plates whichare attached to the brick at the time of pressing, single plates, ordouble plates may be present in the joints together with the asbestosinserts.

It will be understood that the refractory used is preferably of the typesuited for use without kiln firing. The molded brick are cured and/ordried and are then suitable for use. The external plates 38 on theunfired refractory brick tend to protect the brick during shipment.

In some cases separate oxidizable metallic spacer plates are inserted onthe transverse faces.

In some cases the invention is applied to a sprung arch having nohangers as in FIGURE 3. Except for the absence of hangers and hangersockets, and the use of two internal lines of plates 37 in each brick,the construction of FIGURE 3 conforms with that of FIGURES l and 2.

When reference is made herein to oxidizable metallic plates, it isintended to mean continuous plates as opposed to mesh or screen.

In view of my invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part of the benefits of myinvention without copying the method and structure shown, and Itherefore claim all such insofar as they fall within the reasonablespirit of and scope of my claims.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

l. A refractory roof of curved arch form, comprising skewbacks in spacedrelation, and between the skewbacks a plurality of tapered basicrefractory roof brick each having two non-parallel radial sides, saidbrick being of the class consisting of magnesia and mixtures of chromiteand magnesia containing at least 10 percent magnesia by weight, therebeing in each of the brick an oxidizable metallic internal plate inintimate contact with the refractory of the brick extending through theinterior of the brick at a position remote from the outside of the brickin a radial plane over a major portion of the longitudinal and lateraldimension of the brick from a position adjacent the hot end, and therebeing in each radial joint between bricks in the direction of the loadin the arch an oxidizable metallic continuous plate extending over amajor portion of the longitudinal and lateral dimension of the brick,whereby on oxidation of the internal plates their resulting oxidediffuses into the brick leaving open spaces for thermal expansion wherethe internal plates were initially present and reacts with amounts ofthe magnesia present to form a magnesioferrite structure resistant tospalling, and the plates at the radial joints on oxidation produce oxidewith positive dimensional increase.

2. A refractory roof of claim 1, in which there are a plurality ofplates extending in radial planes through the interior of each brick inthe arch.

3. A refractory roof of claim 1, in which there are external oxidizablecontinuous metallic plates on all four lateral joints between adjoiningbricks.

4. A refractory roof of claim 1, in combination with separators ofasbestos interposed between brick at radial joints near the hot end.

References Cited in the file of this patent UNITED STATES PATENTS2,105,804 Beall Jan. 18, 1938 2,236,920 Robertson Apr. 1, 1941 2,547,322Heuer Apr. 3, 1951 2,641,207 Pollen June 9, 1953 ,799,233 Heuer July 16,1957 2,903,254 Heuer Sept. 8, 1959

